Vapor recovery systems in fuel filling installations are already known in the state of the art. These systems comprise a bellows element the purpose of which is to form a seal between the delivery gun and the fuel filler pipe of the motor vehicle tank to be filled, together with a further tube which leads from the dome of the underground tank of the fuel filling installation to said motor vehicle tank to recover the vapor from the tank with or without the aid of a suction pump.
Such known systems have however a series of drawbacks, the most important of which is the critical nature of the necessary hermetic seal to be provided by said bellows, which requires precise and relatively laborious fitting and continuous maintenance.
In this respect, if the bellows does not form a perfect seal, not only is there a considerable fall-off in the efficiency of the system as not all the vapor is drawn in, but precarious safety conditions also arise, especially if a vapor suction pump is used. The now possible uncontrolled in-drawing of air could dilute the vapor-air mixture too much, which as is well known, would make it a critical explosion zone. To overcome this difficulty, known delivery guns have been provided with a device for shutting off delivery if the seal is not perfect (no seal, no flow). Such devices have not encountered favor with the user, in particular in self-service stations, who tends to break their connection by damaging them, with resultant system inefficiency and danger.
A further drawback of known systems is the difficulty of providing the underground tank of the installation, which is at a lower temperature than the vehicle fuel tank, with the specific air quantity necessary to compensate the reduction in volume of the recovered vapor determined by the lower local temperature. This could result in vacuum in the dome of the underground tank, and which, although being a normal and not dangerous condition in installations without vapor recovery, becomes very dangerous in known installations incorporating recovery in which the recovery circuit directly feeds the dome of the underground tank, because of the possible repeated and uncontrolled absorption of air due to seal defects, leading to the aforesaid consequences.
A further drawback is the fact that in known recovery systems using suction pumps or injectors, any suction excess not only produces the aforesaid explosion dangers but can also generate a pressure in the underground tanks which is deleterious from the environmental protection aspect due to possible leakages from the tanks.
The object of the present invention is to obviate said drawbacks by providing a system for the safe recovery of vapor, particularly suitable for fuel filling installations, which does not use any bellows-type seal element and which ensures effective and complete vapor recovery without any danger of explosion or undersirable pressurization of the underground tank.